1. Field of the Invention
The present invention relates to a head suspension of a hard disk drive incorporated in an information processor such as a personal computer.
2. Description of Related Art
A head suspension of a hard disk drive includes a load beam, a head supported with the load beam, and a slider attached to the head. The head suspension has a shock property that determines a lift of the slider from the surface of a hard disk when a shock is applied. The shock property of the head suspension is dependent on the weight of the load beam.
For example, a first head suspension has a load beam having a thickness (t) of 51 μm, a length (lL) of 7 mm, and a gram load of 2.5 gf that is applied by the load beam to a head, and a second head suspension has a load beam having a thickness (t) of 30 μm, a length (lL) of 5.5 mm, and a gram load of 2.5 gf. If a shock of 1 msec duration (1 msec in half wavelength) is applied to these head suspensions, a slider of the first head suspension lifts at an acceleration of 628 G and a slider of the second head suspension lifts at an acceleration of 1103 G.
It is understood from these examples that, to improve the shock property of a head suspension, a load beam of the head suspension must be thin and short and must have a large gram load.
FIG. 14 is a plan view showing a head suspension 101 for a hard disk drive according to a related art. The head suspension 101 has a base plate 103, a load beam 105, and a flexure 107. The load beam 105 has a rigid part (stiff part) 109 and a resilient part (hinge) 111. Each side edge of the rigid part 109 is provided with a rail 113 that rises from the surface of the rigid part 109.
FIG. 15 is a sectional view partly showing a hard disk drive in which the head suspension of FIG. 14 is installed. A carriage 115 has arms 117. To one of the arms 117, the base plate 103 of the head suspension 101 is fixed by, for example, swaging.
The carriage 115 is turned around a spindle 119 by a positioning motor 118 such as a voice-coil motor. The carriage 115 is turned around the spindle 119, to move a head 121 of the head suspension 101 to a target track on a hard disk 123.
When the disks 123 are rotated at high speed, the head 121 slightly rises from the surface of the disk 123 against the gram load of the head suspension 101.
To improve the shock property of the head suspension 101, the length (lL) of the load beam 105 is shortened and thinned, thereby reducing the weight of the load beam 105.
In practice, the arm 117 vibrates. Accordingly, the load beam 105 must be designed in consideration of the first bending frequency of the arm 117, i.e., the resonant frequency of the arm 117 in a first bending mode. The first bending frequency is hereinafter referred to as the “B1 frequency.” It is important to consider the B1 frequency of the arm 117 when determining a B1 frequency for the load beam 105.
FIGS. 16 to 18 are graphs showing a relationship between the B1 frequency and shock property of an arm installed in a 2.5-inch hard disk drive. Among the figures, FIG. 16 shows an acceleration representative of a shock applied to the hard disk drive at which a slider lifts, FIG. 17 shows a maximum acceleration occurring at a front end of the arm due to the applied shock, and FIG. 18 shows a maximum displacement of the arm due to the applied shock. In each of FIGS. 16 to 18, an abscissa indicates the B1 frequency of the arm. In each of FIGS. 16 and 17, an ordinate indicates an acceleration on the arm. In FIG. 18, an ordinate indicates a displacement of the arm. The magnitude of acceleration of the applied shock is 300 G in each case. Half-wavelength durations of the applied shock are 2 msec, 1 msec, and 0.4 msec.
It is understood in FIGS. 16 to 18 that the arm is substantially immovable against a shock of 2 msec or 1 msec duration if the B1 frequency of the arm is high (for example, 1.5 kHz) as indicated with curves 125A, 125B, 125C, 127A, 127B, and 127C. On the other hand, the arm differently acts against a shock of 0.4 msec duration, as indicated with curves 129A, 129B, and 129C.
This is because the arm conducts a large action with respect to a shock of 0.4 msec duration even if the B1 frequency of the arm is high.
A head suspension attached to such an arm must follow the arm action. If the load beam of a head suspension can follow the vibration of an arm, the slider of the head suspension will not lift from the surface of a disk.
Another consideration to be done for a head suspension is an off-track property. It is basically understood that the vertical rigidity (or stiffness) of a head suspension is irrelevant to the off-track property of the head suspension.
In practice, head suspensions involve a slight twist, and disks involve a slight inclination. Due to such twist and inclination, the vertical rigidity or B1 frequency of a head suspension influences the off-track property of the head suspension.
FIG. 19 is a graph showing the off-track property of a head suspension whose B1 frequency is 3.1 kHz. In FIG. 19, an abscissa indicates the frequency of an arm and an ordinate indicates off-track displacement. In the graph of FIG. 19, a curve depicted with a continuous line represents the off-track property of a head suspension measured on a 2.5-inch disk rotated at 5400 rpm and a curve depicted with a dotted line represents the off-track property of the head suspension measured on a 2.5-inch disk rotated at 7200 rpm.
In FIG. 19, the head suspension has a low B1 frequency of 3.1 kHz, and therefore, the bending mode of the head suspension overlaps the bending mode of the arm. As a result, an off-track phenomenon is observed at 3.0 kHz and at 3.3 kHz.
To avoid the off-track phenomenon, the B1 frequency of the load beam of the head suspension must be increased so that the bending mode of the head suspension will not overlap the bending mode of the arm.
To increase the B1 frequency of a load beam, continuously forming the rail 113 along each side edge of the rigid part 109 as shown in FIG. 14 is effective.
For a load beam having a configuration shown in FIG. 20, it is difficult to form a continuous rail along the whole length of a rigid part 109A.
FIG. 20 is a perspective view showing a head suspension. Parts of FIG. 20 corresponding to those of FIG. 14 are represented with the same reference numerals plus “A.”
To improve the vertical rigidity (stiffness) of the load beam 105A, the head suspension 101A of FIG. 20 has rails 113A on the rigid part 109A of the load beam 105A. Abase end of the rigid part 109A has a wide part 131. The wide part 131 has a trapezoidal shape that gradually widens toward a resilient part 111A. The wide part 131 has no rails.
The head suspension 101A of FIG. 20 is used for a 3.5-inch hard disk that has little demand for an improved shock property but has a more intense need for a high sway frequency. To achieve a higher sway frequency, the rigid part 109A is provided with the wide part 131. It is not strongly required for this head suspension to extend the rails 113A over the wide part 131.
A head suspension used for a 2.5-inch disk drive is required to have an improved shock property. The structure of FIG. 20 having no rails on the wide part 131 demonstrates a low B1 frequency for the load beam 105A, to hardly satisfy the required shock property.
To satisfy the required shock property, a structure shown in FIG. 21 may be devised from the structure of FIG. 20. FIG. 21 is a perspective view showing a head suspension 101B. Parts of FIG. 21 that correspond to those of FIG. 20 are represented with the same reference numerals plus “B” instead of “A.”
The head suspension 101B of FIG. 21 continuously forms rails 113B from the front end of a rigid part 109B to the end of a wide part 131B. This configuration can improve the B1 frequency of a load beam 105B to satisfy a required shock property and improve a sway frequency.
Continuously forming the rails 113B from the front end of the rigid part 109B to the end of the wide part 131B involves a longitudinal curve 133 at an intermediate part of each rail 113B. When forming the rail 113B by bending the rigid part 109B including the wide part 131B, the rail 113B may be deformed at the longitudinal curve 133, to twist the rigid part 109B. The twist of the rigid part 109B deteriorates the off-track property of the head suspension 101B.
For the details of the above-mentioned related arts, U.S. Patent Publication No. 6765759B2 and Japanese Unexamined Patent Application Publication No. Hei-9-282624 can be referred to.